Face-milling method and apparatus

ABSTRACT

A face-milling tool includes a milling body forming seats arranged around an axis of rotation of the body. The seats carry identical inserts, each insert being of tetragonal or pentagonal, or hexagonal shape. Each insert includes first and second side faces. Each side face includes a pair of minor cutting edges at each corner of the insert. Two major cutting edges intersect respective ones of the minor cutting edges whereby each major cutting edge and its associated minor cutting edge together form a cooperating pair of cutting edges. There are two of those cooperating pairs at each corner of each side face, whereby there are at least sixteen cooperating pairs on the insert. The minor cutting edges, which function to generate a surface on a workpiece, are sharper than the major cutting edges. During a milling operation the insert is oriented so that only one cutting corner engages a workpiece, and only one of the cooperating pairs of cutting edges of that cutting corner is active.

RELATED INVENTION

This application is a divisional of commonly assigned U.S. Ser. No.08/953,640 filed Oct. 17, 1997.

BACKGROUND OF THE INVENTION

The present invention relates to a tool and a cutting insert for facemilling, and to a face-milling method. The insert includes two parallelside faces interconnected by an edge surface structure. The insert hasfour, five, or six cutting corners. Disposed at each of the corners is apair of cutting edges comprising a minor cutting edge and a majorcutting edge, wherein a minor cutting edge generates a surface on aworkpiece during a milling operation.

PRIOR ART

Through British Patent 951,624 there is previously known a tool and anindexable cutting insert substantially of the above-captioned type,wherein the tool is provided such that both minor cutting edges in arespective cutting corner portion of the cutting insert come intoengagement with the workpiece during the machining operation. This meansthat both minor cutting edges in the corner portion are wornsimultaneously and therefore for example a tetragonal cutting insert canbe indexed, at most, to eight positions (i.e., four positions on eachside) having new cutting edges. U.S. Pat. No. 4,616,962 discloses amilling insert with four cutting edges.

OBJECTS OF THE INVENTION

One object of the present invention is to provide a tool for facemilling, wherein at least sixteen new cutting edges can be utilized.

Another object of the present invention is to provide a cutting insertfor face milling, having cutting edges which makes utilizationeconomically advantageous.

Still another object of the present invention is to provide a cuttinginsert according to an alternative embodiment which is developed fordeflecting the chips in a direction which creates little contactsurface, and subsequently a low friction, between the chip and thecutting insert.

These and other objects have been achieved by an indexable face-millingmetal-cutting insert which comprises two substantially parallel sidefaces interconnected by an edge surface structure to define at leastfour, and not more than six, cutting corners. An intersection of theedge surface structure and the side face at each of the cutting cornersforms a pair of minor cutting edges intersecting one anothersubstantially at a bisector of the cutting corner to form an obtuseangle therebetween. An intersection of the edge surface structure andthe side face at locations between adjacent ones of the cutting cornersforms major cutting edges at both of the adjacent cutting corners. Eachmajor cutting edge intersects an associated one of the minor cuttingedges, whereby each major cutting edge and its associated minor cuttingedge together define a cooperating pair of cutting edges. The insert isindexable to bring only one of the cooperating pairs at a time intocutting relationship with a workpiece, with the side face being operableas a chip surface, and the edge surface structure being operable as aclearance surface. There are two of the cooperating pairs at each of thecutting corners and the pairs are disposed on opposite sides of thecorner bisector.

The invention also relates to a face milling tool which comprises amilling body defining a longitudinal axis and having a plurality ofseats arranged around the axis. Indexable metal cutting inserts similarto the type described above are mounted in respective ones of the seats.Another aspect of the invention involves a face-milling method employinginserts similar to those described above.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and advantages of the invention will become apparent fromthe following detailed description of preferred embodiments thereof inconnection with the accompanying drawings in which like numeralsdesignate like elements, and in which:

FIG. 1 shows a tetragonal cutting insert according to the presentinvention in a plan view;

FIG. 2 shows the cutting insert of FIG. 1 in a side view;

FIG. 3A shows the cutting insert in a cross-section according to lineIII—III in FIG. 1;

FIG. 3B shows an enlargement of a fragment of FIG. 3A;

FIG. 4 shows the cutting insert in a cross-section according to lineIV—IV in FIG. 1;

FIG. 5 shows an alternative embodiment of a tetragonal cutting insertaccording to the present invention in a plan view;

FIG. 6 shows the alternative cutting insert in a side view;

FIG. 7 shows the alternative cutting insert in a cross-section accordingto line VII—VII in FIG. 5;

FIG. 7A shows an enlargement of a fragment of the insert of FIG. 7;

FIG. 7B is a view similar to FIG. 7A of yet another embodiment of theinvention;

FIG. 8 shows a milling tool and insert according to the presentinvention in a side view making a cut;

FIGS. 9 and 10 show magnifications of the tool's active corner for thetwo insert alternatives of FIGS. 1 and 5, respectively, as seen towardsthe plane of the active side faces of the cutting insert; and

FIG. 11 shows an additional embodiment of a cutting insert according tothe present invention in a plan view.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

With reference to FIGS. 1-4, 8 and 9, there is shown a metal-cuttinginsert 11 for face milling according to the present invention. Thecutting insert comprises a matrix of sintered, preferably coated,cemented carbide and has a polygonal basic shape, in this case atetragonal basic shape. The cutting insert may alternatively bepentagonal or hexagonal. The cutting insert 11 comprises two,essentially parallel side faces 12, 13 interconnected by an edge surfacestructure comprised of edge surfaces 14A-14D. The side face 13 isidentical to the side face 12, and therefore only one side face isdescribed hereinafter. The cutting insert 11 has a negative geometry,i.e., the edge surface structure perpendicularly intersects the sidefaces. However, it is possible within the scope of the invention for thecutting insert to have a double positive geometry, i.e., each edgesurface would form an acute angle with a respective side face and thusforms a central circumferential recess in each of the edge surfaces14A-14D.

Major cutting edges 15 are formed by intersection of the side face 12with respective edge surfaces 14A-D. In each cutting corner 17 locatedbetween two adjacent edge surfaces, there has been providedsubstantially planar or somewhat cambered bevel surfaces which form partof the edge surface structure. For example, between the edge surfaces14A and 14B there are provided two bevel surfaces 18A, 18B disposed onopposite sides of the corner bisector B. The edges formed by theintersection of the side face 12 with the respective bevel surface 18Aor 18B are called minor cutting edges 16. One of the edges 16 willgenerate a surface on the workpiece 40 during a face milling operationby being arranged parallel to the surface of the workpiece (or arrangedperpendicular to the axis of the rotation of the milling tool). One ofthe major cutting edges 15 is intended to cut the major part of thematerial in the form of chips during the face milling operation.According to the invention, only one major cutting edge 15 and one minorcutting edge 16 will be in engagement with the workpiece simultaneouslyand thereby these two edges work in pair and define a cooperating pairof cutting edges. Each minor cutting edge 16 forms an acute externalangle a with a projection of an associated major cutting edge 15 asviewed in a direction perpendicular to the side face 12. The angle alies in the interval 38° to 42°, preferably around 40°.

Each major cutting edge 15 inwardly connects to a chip-upsetting surfaceor primary bevel 19, FIG. 3B, which constitutes the most peripheral partof the side face 12. The primary bevel is negatively angled and does notextend along the cutting corner 17, since the minor cutting edge 16 mustbe as sharp and as easy-cutting as possible. That is, a suitable edgeradius on the minor cutting edge 16 is chosen, whereby the minor cuttingedges are sharper than the major cutting edges. A first concave chipforming surface 20 is situated inside the chip-upsetting surface 19. Asecond concave chip forming surface 21 is situated inside the minorcutting edge 16 in the cutting corner. The second chip forming surface21, FIG. 4, is shallower than the first chip forming surface 20, forshaping the chips during the face milling operation. An area 22 isprovided in the side face 12, symmetrically about the corner bisector Bto further form favorable chips and for best supporting the cuttingcorner.

In side view, it is evident that the minor cutting edges 16 are providedin planes oriented parallel with the side faces but somewhat below theassociated side face. Each minor cutting edge 16 connects to theassociated major cutting edge 15 via a radius R1. Alternatively theradius R1 can be replaced by a number of planar facets which togetherform a curve. The expression “cooperating” major cutting edge and minorcutting edge refers to a pair of major and minor cutting edges whichcooperate during milling and which are physically connected to eachother, possibly via a radius. The two minor cutting edges 16 of eachcutting corner together form an obtuse inner angle ε, which is about170° and the minor cutting edges are mirror-imaged or symmetrical aboutthe bisector B.

Adjacently disposed bevel surfaces 18A, 18B intersect along a line E,which coincides with the plane of the bisector. Each major cutting edge15 is concavely curved with a radius R2 to form a somewhat positiveaxial angle even though the cutting insert has been mounted negative inthe milling body. The radius R2 is longer than the length L of the sideof the cutting insert. The largest distance D between the major cuttingedge and the plane of the connected side face is at the midline M of themajor cutting edge, said distance being smaller than 1 mm but biggerthan 0.4 mm.

To be able to use all 16 cutting edge pairs (eight pairs per sidesurface) in the most optimal manner, the major cutting edge 15 should beused not more than to its center point C, i.e., to the middle of thecutting insert during a milling operation (see FIG. 8). This means thatthe cutting depth A (see FIG. 8) should not be so great as to cause morethan one half of the major cutting edge 15 to engage the workpiece 40,i.e., the cutting depth should maximum be A=(L/2)(sin K), where K is thesetting angle (see FIG. 8). As a result only one of the minor cuttingedges 16 engages the workpiece.

With reference now to FIGS. 5-7 an alternative embodiment of aface-milling cutting insert 11′ is shown according to the presentinvention. The same items in the alternative embodiment have been giventhe same reference numbers with a prime symbol. The cutting insert 11′is different from the earlier described cutting insert in that itcomprises a number of recesses 23′ in each concave chip forming surface20′, which recesses are spaced along the major cutting edges 15′ andextend essentially laterally relative to the associated major cuttingedges 15′. No recesses 23′ are located in the cutting corners. Therecesses are provided in groups of seven or the like, the groupsdisposed on opposite sides of the mid-line M′ of the cutting insert.Crests 24′ are situated between the recesses 23′ in the chip formingsurface 20′, each crest 24′ bridging adjacent recesses 23′ in adirection along the associated major cutting edge 15′. The recesses 23′do not extend perpendicularly to the cutting edge 15′ but they ratherform an acute angle β′ with a line extending perpendicular to theassociated cutting edge 15′, such as shown in FIG. 5. The angle β′ is inthe interval of 5°-55°, preferably in the interval of 10°-20°. A mostpreferred value for the angle β′is 15°. An advantage with this type ofchip former is that relatively little heat is transferred to the cuttinginsert from the chip and therefore problems which relate to hightemperatures in the cutting edge 15′, such as plastic deformation and/ordiffusional wear, are avoided. This limits the wear of the cutting edgeand results in better tool life also at high temperatures. Such a typeof chip forming is more closely described in U.S. Pat. No. 5,074,720which is hereby incorporated herein by reference for a description ofchip forming.

In FIG. 8 there is shown a face milling cutter according to the presentinvention, including a milling body 30 intended to be rotated in amilling machine about an axis CL. The milling body comprises a number ofseats for receiving tetragonal, pentagonal or hexagonal cutting inserts,such as the tetragonal insert 11 or 11′. A conventional adjustmentdevice 31 is provided in order to facilitate fine adjustment of thecutting insert in the cutting insert pocket. The cutting insert isprovided to be clamped in a known manner with a clamp after fineadjustment has been made. As is apparent from the figure, thecooperating major cutting edge 15A and minor cutting edge 16A areprovided on the same side of the bisector B. The active minor cuttingedge 16A is arranged substantially perpendicular to the axis of rotationCL of the face milling cutter. The minor cutting edge 16A (FIG. 9)generates the surface of the workpiece while the other minor cuttingedge 16B is spaced at a distance from the workpiece surface by forming aclearance angle with said surface. The tool has a setting angle K, whichis maximum 42°. The major cutting edge 15A is provided to cut the majorpart of the material which shall be machined in the form of chips andshould therefore be reinforced by means of the chip-upsetting surface19, while the minor cutting edge 16A constitutes a finish cutting edgeand should therefore be sharper than the major cutting edge 15A.

In FIGS. 8 and 10 the cutting inserts 11 and 11′, respectively, areshown in engagement with the workpiece 40. The tool works with a settingangle K or K′ of about 40°.

FIG. 11 shows a pentagonal cutting insert 11″, wherein the setting angleK″ is chosen in the interval of 15° to 30°, preferably between 20° and25°. The cutting insert 11″ has twenty pairs of cooperating cuttingedges 15″, 16″.

Thus the present invention relates to a method, a tool and a cuttinginsert for face milling wherein at least sixteen new cutting edges canbe utilized. The cutting insert has at least eight pairs of cuttingedges to be used in one rotational direction and at least eight pairs ofcutting edges to be used in an opposed rotational direction, which makesutilization of the insert economically advantageous.

The invention is in no way limited to the above described embodiments.For example the basic shape of the cutting insert be pentagonal orhexagonal. In addition the recesses 23′ may be replaced by projections123′ of similar shape as shown in FIG. 7B. Also in other respects theinvention can be freely varied within the limits of the appended claims.

What is claimed is:
 1. A method of performing a face-millingmetal-cutting operation using an insert comprising two substantiallyparallel side faces interconnected by an edge surface structure todefine at least four and not more than six cutting corners; anintersection of said edge surface structure and each of said side facesat each of said cutting corners forming a pair of minor cutting edgesintersecting one another substantially at a bisector of said cuttingcorner to form an obtuse angle therebetween; an intersection of saidedge surface structure and each of said side faces at locations betweenadjacent ones of said cutting corners forming major cutting edges atboth of said adjacent cutting corners; each major cutting edgeintersecting an associated one of said minor cutting edges, whereby eachmajor cutting edge and its associated minor cutting edge together definea cooperating pair of cutting edges; there being at least eight of saidcooperating pairs on each of said side faces; each side face includingtwo of said cooperating pairs at each of said cutting corners anddisposed on opposite sides of said corner bisector; the methodcomprising the steps of bringing one cutting corner of one of said sidefaces into cutting relationship with a metallic workpiece while rotatingsaid insert, and while orienting said insert such that only one of saidcooperating pairs of cutting edges at said one cutting corner is in saidcutting relationship; said one side face functioning as a chip face, andsaid edge surface structure functioning as a clearance surface, saidminor cutting edges being sharper than said major cutting edges.
 2. Aface-milling tool comprising a rotary milling body defining alongitudinal axis and having a plurality of seats arranged around saidaxis; and indexable metal-cutting inserts mounted in respective ones ofsaid seats, each of said inserts comprising two substantially parallelside faces interconnected by an edge surface structure to define atleast four and not more than six cutting corners; an intersection ofsaid edge surface and each of said side faces at each of said cuttingcorners forming a pair of minor cutting edges intersecting one anothersubstantially at a bisector of said cutting corner; an intersection ofsaid edge surface structure and each of said side faces at locationsbetween adjacent ones of said cutting corners forming major cuttingedges at both of said adjacent cutting corners; each major cutting edgeintersecting an associated one of said minor cutting edges, whereby eachmajor cutting edge and its associated minor cutting edge together definea cooperating pair of cutting edges; there being at least eight of saidcooperating pairs on each of said side faces; each side face includingtwo of said cooperating pairs at each of said cutting corners, said twopairs disposed on opposite sides of said corner bisector; said bodybeing oriented to bring one cutting corner of one of said side facesinto cutting relationship, and with only one of said cooperating pairsof said one cutting corner being in cutting relationship; said one sideface arranged to function as a chip face, and said edge surfacestructure arranged to function as a clearance surface, said minorcutting edges being sharper than said major cutting edges.
 3. The toolaccording to claim 2 wherein said tool has a setting angle no greaterthan 42 degrees.
 4. The tool according to claim 2 wherein said minorcutting edges at each of said corners together form an obtuse angle. 5.The tool according to claim 2 further including concave chip formingsurfaces disposed inwardly of said major cutting edges, each chipforming surface including a row of recesses, each row extending in adirection forming an acute angle of 5 to 55 degrees with a lineextending perpendicular to the associated major cutting edge.
 6. Theinsert according to claim 5 wherein the acute angle is 10 to 20 degrees.7. The insert according to claim 6 wherein the acute angel is about 15degrees.
 8. The insert according to claim 2 wherein each of said sidefaces includes a planar land disposed between each of said major cuttingedges and its respective chip forming surface; each of said minorcutting edges directly intersecting its respective chip forming surface,said land having a constant width.